Lead zirconate titanate (referred to as “PZT” hereinafter) that contains lead is a piezoelectric material most widely used in various piezoelectric devices. Attempts have been made to replace lead-containing piezoelectric materials by lead-free piezoelectric materials. This is to address the concern that lead-containing piezoelectric devices once discarded and exposed to acid rain may inflict damage on ecosystem as the lead component in the piezoelectric materials may leach into earth. Thus, various proposals of piezoelectric material have been made.
One example of the lead-free piezoelectric material is a strontium calcium sodium niobate (SCNN) having a tungsten bronze structure. PTL 1 discloses a technique of improving the piezoelectric property by adding a rare earth element to SCNN. PTL 2 discloses a technique of improving the piezoelectric property by replacing Na sites with K. However, since the unit cell of crystals having a tungsten bronze structure has a high shape anisotropy, the polar axis direction lies only in the c-axis direction, i.e., the short side direction. Accordingly, there have been fewer effective domains that can contribute to piezoelectricity and the piezoelectric properties have been unsatisfactory.
NPL 1 discloses a technique of improving the characteristics of SCNN by orienting SCNN by using a magnetic field (magnetic orientation). Magnetic orientation can increase the number of effective magnetic domains that contribute to piezoelectricity. NPL 2 discloses an example of fabricating a prototype ultrasonic motor by using magnetically oriented SCNN. However, this ultrasonic motor requires application of a voltage about 10 times greater than that required by a PZT ultrasonic motor and has unsatisfactory characteristics.
The present invention provides a lead-free strontium calcium sodium niobate-based tungsten bronze structure metal oxide having a high degree of orientation and high piezoelectric property. A piezoelectric element, a liquid discharge head, an ultrasonic motor, and a dust cleaning device that use the piezoelectric material are also provided.